The invention concerns the processes for production of plastic laminates with metal laminae.
Generally plastic laminates consist of sheets formed of several layers of plastic materials, assembled together in a stable manner, usually by pressing, on a base of paper, fabric, fiber glass or other materials. The plastic materials may be of phenol, melamine, epoxy, polyester, silicon, fluoride or others.
In the production of printed circuits a metal lamina, usually of copper, is made to adhere to one or both sides of a plastic laminate during the pressing process.
A pile of packages, all virtually the same, is formed; each of these comprising a number of sheets, impregnated with plastic materials, and copper laminae one of which is placed on each side of each package.
A sheet of metal, stainless steel or some other kind, is placed between each package, and the pile so formed is put inside a multiple-plate press that provides heat and pressure simultaneously.
When each heat cycle, in which a temperature of 190.degree. C. may be reached at pressures of up to 100 kg/cm.sup.2, lasting over 100 minutes and including a cooling stage down to 70.degree.-80.degree. C., has been terminated, a compact and rigid product is obtained whose single components are closely associated.
Presses suited to this kind of production must necessarily be complex and have a low output because of their many heating plates and they produce heat and pressure at the same time in well-defined and accurate sequences, according to their needs to create, by conduction, uniform temperatures throughout the various packages in the pile of which obviously only those at the top and bottom will be in contact with the heating plates.
Particularly, the conduction of heat from the press's heating plates to the plied up packages, and vice versa during the cooling -stage, is greatly hindered because of intervening components made of fiber glass impregnated with plastic materials, or others equally insulating, which are known to be very poor conductors of heat, in the packages above and below such material in the pile.
In addition to complicating the structure of the press, the presence of many heating plates slows down loading and unloading of packages, while problems are created for short runs of production, these being relatively more costly.